Method for grooving the bore of a tube and grooving tool-holder

ABSTRACT

A process to produce alternately concave and convex grooves that are evenly spaced inside a tube, wherein said process comprises the following steps: at least one simultaneous broaching stage for all said grooves of said tube using at least one roughing tool and/or at least one finishing tool, said being tools made integral with a handle bar using linking means, said different roughing tools being implemented successively and having a convex profile that gradually approaches the concave profile of said grooves, at least one finishing tool having a concave profile to make the convex profile of said grooves.

The technical scope of the present invention is that of processes to shape and thread the inner wall of tubes, and more particularly thermal exchanger tubes made of materials having high mechanical properties.

A process to broach grooves onto the external wall of a cylinder is known namely by U.S. Pat. No. 4,294,568. According to this process, two adjacent grooves are simultaneously broached, one using a roughing tool and the other using a finishing tool. The roughing tool has a staggered profile and the finishing tool matches the final profile of the groove. If this process enables grooves to be made that have a complex profile, it cannot be adapted to the simple and fast production of complex rifling on the inside of a tube.

U.S. Pat. No. 4,411,569 also discloses a broaching process for the rifling of a gun barrel in which several broaches are axially joined to a rod whilst being free to rotate. The traction of the rod machines the grooves. Each broach has a different profile: the first broach ensures a rough machining and the last ensures the finishing. The drawback to this process lies in that it can only be used to produce a groove with a simple profile. It cannot be used to make a groove having a complex profile covering all the internal surface of the barrel and comprising a succession of concave and convex profiles.

The aim of the present invention is to economically produce the internal profile of a tube and namely a metallic tube having high mechanical properties, made of refractory steel, for example, which is complex in shape namely comprising a succession of grooves with a concave profile separated by convex profiles.

The invention thus relates to a process to produce alternately concave and convex grooves that are evenly spaced inside a tube, such process wherein it comprises at least one simultaneous broaching stage for all the grooves of the tube using at least one roughing tool and/or at least one finishing tool, tools made integral with a handle bar using linking means, the different roughing tools being implemented successively and having a convex profile that gradually approaches the concave profile of the grooves, at least one finishing tool having a concave profile to make the convex profile of the grooves.

According to one implementation of the process, at least one roughing or finishing tool has at least one tip enabling the concave or convex profile of the grooves to be produced.

Each tip making the concave profile may advantageously be circular and will have a radius equal to the groove that must be machined.

According to another implementation of the process, at least one roughing or finishing tool is single-piece.

The bar may incorporate a guiding way with respect to the tube.

One application of the process aims to produce grooves inside a tube of a diameter less than or equal to 38 mm, each roughing and finishing tool being single-piece.

Another application of the process aims to produce grooves inside a tube of a diameter greater than 38 mm, each roughing and finishing tool having add-on tips.

Another application of the process aims to produce longitudinal grooves inside a tube where the bar is driven only in translation or else to produce helicoidal grooves when the bar is driven in translation and in rotation.

The invention also relates to a tool holder for the production of grooves inside a tube, such tool holder comprising at least two offset tools integral with a bar and separated two by two by at least one spacer.

According to one characteristic, the spacers are in the form of smooth tubes.

According to another characteristic, each spacer comprises a tube having radial straight vanes delimiting housings between each other.

The straight vanes will be of a width such that they come into contact with the internal surface of the tube before the grooves are machined.

Each spacer will thus be integral with the bar.

A first advantage of the process according to the invention lies in its capacity of producing an internal profile of a complex shape.

Another advantage lies in the capability of grooving tubes of substantial length or around 2 to 6 m.

Another advantage lies in the fact that the process enables the required profile to be economically produced.

Other characteristics, particulars and advantages of the invention will become more apparent from the description hereafter given by way of illustration and in reference to the drawings, in which:

FIG. 1 shows the grooving profile of a tube obtained using the process according to the invention,

FIG. 2 schematically shows a machine tool enabling the process according to the invention to be implemented,

FIG. 3 is a section illustrating an embodiment of a tool holder,

FIG. 4 illustrates another embodiment of the tool holder,

FIG. 5 is a cross section of a tool holder in accordance with FIG. 4,

FIG. 6 shows a view of a spacer used in the invention,

FIGS. 7 to 9 show different possible offset tools.

FIG. 1 partially shows a tube 1, for example the metallic tube of a thermal exchanger with high mechanical properties, made of refractory steel, for example. This tube 1 is firstly pierced following a substantially cylindrical profile 2. The final grooving profile required incorporates a succession of concave-profiled grooves 3 separated by convex-profiled crests 4. The global profile obtained in accordance with the invention has the particularity of covering the whole internal surface of the tube 1. The grooves 3 and crests 4 here have a circular profile with a radius R. The maximal depth X of the groove is less than or equal to 2R. It is naturally possible for profiles to be produced that have a different radius for the concave and convex grooves.

It goes without saying that the grooves 3 may be made along a generating line of the tube at an angle that is nil or different from zero with respect to the generating line so as to be straight or helicoidal. In the first case, the tool has a translational movement and in the other, both a translational and rotational movement. In the latter case, the teeth of the offset tool will be inclined at an angle equal to the angle of the helicoidal groove with respect to the tube's generating line.

FIG. 2 schematically shows a machine tool enabling the process according to the invention to be implemented. The machine comprises a bed 6 onto which the cylindrical tube 1 to be threaded is flanged. This bed incorporates a bar 5 connected to a bar holder head 8 of the machine enabling a multiple tool holder 9 to be drawn through the cylindrically pre-bored tube 1. The multiple tool holder 9 is attached to the bar 5 linked to the bar holder head 8 using quick linking means 10. The multiple tool holder 9 incorporates at least one roughing offset tool 11 and one finishing offset tool 12 to make the grooves 3 in the tube 1.

The tool holder 9 also incorporates intermediate offset tools 13 and 14 enabling the move from roughing to finishing. Naturally, the other components of the machine are known, and namely those means used to pull the tool 9 and it is thus unnecessary for them to be described more fully.

FIG. 3 shows a first embodiment of a multiple tool holder 9, for example carrying roughing offset tools. By way of example, it incorporates three offset tools 15 each provided with several tips 16. Each offset tool 15 is made integral in rotation with the bar 5 by means of a cleat 17. The offset tools 15 are also linked in translation by spacers 18 in the shape of smooth tubes, and the assembly is placed between two guiding/centring ways 19 and 20. A nut 21 blocks said assembly with respect to the bar 5.

The first guiding/centring way 19 is formed by a part prolonging the bar 5, the second way 20 is formed by a ring. Ways 19 and 20 have an outer diameter substantially equal to the initial diameter of the tube 1. These two ways ensure the guidance of the tool holder 9 in the tube to be threaded. In a known manner, cutting fluid is injected, for example through the bar 5 and the spacers 18 by holes, not shown.

Another embodiment is illustrated in FIGS. 4, 5 and 6. In this embodiment, the smooth spacers are replaced by spacers 22 comprising a tube having radial vanes 24 delimiting housings 25 between each other. Each housing receives the shavings machined by the tip or cutting profile of the tool placed between the two vanes delimiting the housing.

This avoids shavings generated during the grooving operation from accumulating in the lower part of the tube 1 and deteriorating its surface. The spacers 22 are positioned angularly with respect to the tool 9 by cleats 31 such that each tip or cutting profile of the tool is positioned between two successive vanes.

The radial vanes 24 are of a width such that they come into contact with the internal surface of the tube 1 before the grooves are machined. Thus, the vanes press against the crests of the convex profiles and delimit housings 25 to receive the shavings.

In this embodiment, as many vanes are provided as grooves. It goes without saying that the number of vanes can be reduced. The length L of the spacer 22 depends on the length of the bore to be grooved and on the number of offset tools 15 fastened on the bar 5, which the Expert will find easy to determine.

FIGS. 7 to 9 show different offset tools able to be used in the invention: the upper view being a cross section, the lower view a vertical section. The tool 26 show in FIG. 7 is a roughing tool fitted with 8 convex circular tips 16 of tungsten carbide having a housing 27 for a cleat. These tips 16 enable a concave shape to be given to the groove 3.

The tool 28 shown in FIG. 8 is a finishing offset tool 15 equipped with 8 concave tips 29. These tips 29 enable a convex shape 4 to be given to the grooves. As before, the tool 28 has a housing 27 intended for a cleat.

In any event, the tips 16, 29 are fastened by classical means, not shown, (for example by screwing).

The tools according to FIGS. 7 and 8 are preferably used to groove tubes with a wide internal diameter, for example over 38 mm.

FIG. 9 shows a single-piece tool 30 preferentially used to groove small diameter tubes, for example less than 38 mm.

Somebody skilled in the art will easily determine the number of offset tools to mount on the bar 5 depending on the traction capability of the machine tool, the mechanical properties of the tube's material (machinability) and of the shaving surface taken off at each pass.

By way of an example, a machine developing 7 tons of traction can draw 1 to 6 tools.

According to the geometry of the tube to be machined (initial diameter, depth and number of grooves) a tool holder will need to be used incorporating more or less numerous offset tools of different types (roughing, finishing, concave or convex).

Thus, for a tube having shallow grooves (less than or equal to 5 mm) a tool holder ensuring the roughing and finishing in a single pass may be used. The first offset tools carried by this tool holder will be the roughing offset tools for the concave profile, the last ones will be finishing tools for the convex profile.

For a tube having grooves of greater depth (over 5 mm), several assemblies of tool holders will be needed. The first machining passes will be made with tool holders fitted only with roughing tools for the concave profile.

The last passes will be made with tool holders fitted only with tools (roughing then finishing) machining convex profiles.

By way of example, to produce a grooved bore such as that shown in FIG. 1 (8 grooves of a radius of 5 mm for a depth X of 10 mm made in a tube having a 40 mm diameter smooth bore), 100 offset tools will be needed each carrying 5 mm radius tips, such offset tools for which the relative positions of the tips will be radially displaced with respect to one another so as to ensure a machining pitch of 0.1 mm at the radius between two successive tools.

The final profile will be obtained, from the initial smooth bore, by 50 passes of a tool holder 9 incorporating 1 to 6 offset tools having ever-increasing cutting diameters from one end to the other of the bar.

Somebody skilled in the art will select the number of tools compatible with the power of the machine drawing the tool holder bar.

Note, for example, that for the first machining passes a small surface is shaven off by each offset tool, the number of tools on the tool holder may thus be maximal.

For the last passes, a large shaving is removed at each pass, the machine is under greater strain and the number of tools carried by the traction bar will be reduced.

Machining the convex forms will be carried out after the concave profile has been produced by the passage of a mill fitted with 4 concave shaped tools having ever-increasing relative cutting diameters from one end to the other of the bar 5.

Advantageously, the bar 5 can be made to move in translation so as to create longitudinal grooves or can be made to move in translation and in rotation so as to create helicoidal grooves.

The pitch of the grooves thus obtained depends on the spin rate of the bar with respect to its forward movement. This type of groove may easily be made by numerical control suitably programmed with the ratio of the bar's spin rate over its forward motion. 

1. A process to produce alternately concave and convex grooves that are evenly spaced inside a tube, wherein it comprises at least one simultaneous broaching stage for all the grooves of the tube using at least one roughing tool and/or at least one finishing tool, tools made integral with a handle bar using linking means, the different roughing tools being implemented successively and having a convex profile that gradually approaches the concave profile of the grooves, at least one finishing tool having a concave profile to make the convex profile of the grooves.
 2. A process to produce grooves inside a tube according to claim 1, wherein at least one roughing or finishing tool has at least one tip enabling the concave or convex profile of the grooves to be produced.
 3. A process to produce grooves inside a tube according to claim 2, wherein each tip making the concave profile is circular and has a radius equal to the groove that must be machined.
 4. A process to produce grooves inside a tube according to claim 1, wherein at least one roughing or finishing tool is single-piece.
 5. A process to produce grooves inside a tube according to claim 1, wherein the bar incorporate a guidance way with respect to the tube.
 6. Application of the process to produce grooves inside a tube according to claim 1, wherein for a tube of a diameter less than or equal to 38 mm, each roughing and finishing tool is single-piece.
 7. Application of the process to produce grooves inside a tube according to claim 1, wherein for a tube of a diameter greater than 38 mm, each roughing and finishing tool has add-on tips.
 8. Application of the process according to claim 1 to produce longitudinal grooves inside a tube, wherein the bar is driven only in translation.
 9. Application of the process according to claim 1 to produce helicoidal grooves inside a tube, wherein the bar is driven in translation and in rotation.
 10. A tool holder for the production of grooves inside a tube according to the process in claim 1, wherein it comprises at least two offset tools integral with a bar and separated two by two by at least one spacer.
 11. A tool holder according to claim 10, wherein the spacers are in the form of smooth tubes.
 12. A tool holder according to claim 10, wherein each spacer comprises a tube having radial straight vanes delimiting housings.
 13. A tool holder according to claim 12, wherein the radial straight vanes are of a width such that they come into contact with the internal surface of the tube before the grooves are machined.
 14. A tool holder according to claim 12, wherein each spacer is integral in rotation with the bar.
 15. A tool holder according to claim 10, wherein it incorporates at least two offset tools having at least one convex profile.
 16. A tool holder according to claim 10, wherein it incorporates at least one offset tool having a concave profile. 